Irritator
| Irritator | ||||||||||||
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Skeletal reconstruction of irritator challengeri |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Albium ) | ||||||||||||
| 112.9 to 100.5 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Irritator | ||||||||||||
| Martill et al. , 1996 | ||||||||||||
Irritator is a genus of theropod dinosaur with only one species described ( type species ). Irritator belongs to the spinosaurids , a group of bipedal dinosaurs with a greatly elongated snout and straight teeth. The animal, which is probably up to eight meters long, lived around 113 to 100 million years ago ( Albium ) in the Lower Cretaceous in what is now South America .
Of this dinosaur , only the approximately 80 centimeter long fossil skull has been found in the Romualdo member, a layer part of the Brazilian Santana formation . Since this is very similar to the skulls of Suchomimus and Spinosaurus , it is assumed that he had elongated spinous processes on the vertebrae , like these .
This species is now generally regarded as identical (synonymous) with Angaturama limai , who lived in the same place at the same time and of which only the foremost part of a skull is known.
Fossil description
History and characteristics of the irritator fossil
Irritator was first scientifically described in 1996 by the paleontologists Martill, Cruickshank, Frey, Small and Clarke . This description was based on the finding of a skull, the holotype , from the Santana Formation in eastern Brazil in the southern part of the state of Ceará in the Araripe Basin. He was in the Romualdo layer member, which is assigned to the Lower Cretaceous period .
The find was made by private collectors. They tried to complete the fossil skull with a plaster-like modeling compound, which made the reconstruction by the taxidermists very time-consuming. A computed tomography also showed that the skull was artificially lengthened by attaching parts of the upper jaw to the intermaxillary (premaxillary). Today the fossil is kept in the collection of the State Museum for Natural History in Stuttgart under catalog number SMNS 58022 .
The skull is almost completely preserved and is considered to be the most complete skull find of a spinosaurid. It is characterized above all by its unusually long and curved snout region, which is heavily compressed on the sides. The total length of the full skull is estimated to be around 84 centimeters. It has a distinct sagittal ridge that runs from the forehead over the nasalia to the premaxillary and thus extends over the entire skull; Such a crest can be found in some other dinosaurs, but it is rarely proven for the Theropoda. The nostrils are shifted backwards to almost in front of the eyes and the merging of the intermediate jaw to form a secondary roof of the mouth causes the choane , the inner nostril, to be shifted backwards towards the throat.
The teeth have a unique embedding of the greatly elongated and straight teeth with conical tooth crowns, which indicates a mesolingual tooth change , in which new teeth are pushed between the teeth currently in use; this is currently also assumed for Spinosaurus due to the close relationship . The teeth have lengths of 6 to about 40 millimeters. The upper of the two temporal windows (supratemporal windows) of the skull is almost completely reduced, and other features of the skull anatomy also allow a clear differentiation of Irritator from other known genera. Irritator shares a number of characteristics with Spinosaurus, such as the small number of maxillary teeth and their shape . Many other characteristics can be assumed for higher-level taxa , but cannot be verified due to the often missing skulls.
In 2004, parts of a spinal column, consisting of three cross and six caudal vertebrae , were also found in the Santana Formation , which can be assigned to the spinosaurids due to the structure of the vertebral bodies. It is very likely that these vortices also belong to Irritator , as this is the only known spinosaurid of the formation .
Angaturama limai Kellner & Campos, 1996
Angaturama limai from the same period as Irritator challengeri was first described in February 1996 by Alexander WA Kellner and Diogenes A. Campos, also on the basis of a fossil from the Santana Formation , and is now widely regarded as a synonym for Irritator . Some scientists even assume that the two fossils are parts of the skull of the same individual. Kellner and Campos (2000) and Machado and Kellner (2005), however, take the view that there are two different species and that Angaturama had a significantly higher and laterally more flattened skull as an irritator .
The fossil consists only of the front part of the skull, which is characterized by the fact that it is very narrow and has a premaxillary sagittal crest. In the premaxillary there was a broken tooth with a partially preserved tooth crown, which corresponds to that of an irritator ; The premaxillary had a total of 7 teeth, as can be seen from the tooth sockets, with the third tooth being the largest. The fossil described is now kept under the number USP GP / 2T-5 at the Universidade de São Paulo . It was described as the first known remnant of a dinosaur skull from Brazil , but the description of Irritator challengeri was made at a time when that of Angaturama was still in the technical review and thus actually represented the first description of dinosaurs from the Santana Formation. In the event that Angaturama and Irritator are actually considered to be members of the same species, Irritator challengeri would be the valid scientific name ( priority rule ).
Find locality and paleoecology
The exact location of the irritator fossil is unknown, as the skull was first brought to science through fossil dealers and collectors. The rock mass, which included the skull, the matrix, could be assigned to a rock of the Romualdo member of the Santana formation due to lithological features ; This classification was confirmed by microfossils of crustaceans of the genus Pattersoncypris and fish scales that could be assigned to the Ichthyodectid cladocylus . A survey of the local fossil dealers by the first describer found a site near the village of Buxexé near Santana do Cariri on the flank of the Chapada do Araripe at an altitude of about 650 m above sea level. Since there really rock from the Romualdo Member minded is, this locality is considered to be very likely for the fossil.
The Romualdo member of the Santana formation is commonly due to the fish fauna the Albium assigned and the last section of the lower chalk, whereas the widely used to Biostratigraphie used ostracods (Ostracoda) classified in the Aptian suggest. Accordingly, the layers are around 110 million years old and date from a time when the continents of Africa and South America in the northern part of Brazil were still connected.
The horizon of the Santana Formation, in which both fossils were found, was very likely formed by sedimentation in a shallow inland lake that was filled with fresh or brackish water. With regard to salinity , the fossil discoveries made so far convey an ambivalent picture, the presence of some freshwater fish speaks for salt-free or low-salt water, but forms were also found that are typically marine. The insects found are more an indication of fresh water, the discovery of the turtle Santanachelys gaffneyi, which is adapted to salt water, suggests salt water. The theory that it was a brackish lagoon that was connected to the sea is therefore most widely recognized . The climate was tropical and warm and is said to have largely corresponded to today's climate in Brazil.
Way of life
Irritator challengeri malnourished as those found in large numbers in the Santana Formation pterosaurs probably of fish that he was hunting in the formerly located there lake. Like today's crocodiles , the irritator was probably a food generalist who, in addition to the fish, also ate all other animals that he could catch. A fossilized cervical spine of a pterosaur with a tooth stuck in it, which is assigned to the irritator , is considered to be certain that pterosaurs also belonged to its food spectrum. It is not known whether he captured them as an active hunter or ate dead animals as scavengers.
The elongated and very narrow snout with the relatively uniform, pointed teeth in all spinosaurs indicates a diet that was mainly based on fishing . It is a convergence to many other animal groups that have adapted to fish as food in the course of evolution . This configuration is found primarily in crocodiles (very pronounced in the Ganges and Sunda gavials , for example ), but also in whales and many extinct marine reptiles such as ichthyosaurs , mosasaurs and some plesiosaurs .
The elongated conical teeth, which have no saw edges, are particularly suitable for grabbing and holding on to the entire prey and thus differ from the teeth of carnivores, which have to tear off or cut parts of the prey after grabbing. Far back nostrils and the secondary roof of the mouth also allow breathing when the majority of the elongated snout is under water or when a prey is being held. In particular, the sagittal crest of Irritator is also an indication of pronounced neck muscles, which are necessary to pull the muzzle through the water against the water resistance and to pull the head back quickly. Sues et al. In 2002, however, it became clear that there was no reason to assume that the Spinosauridae have specialized entirely in fishing. Rather, they emphasize that this skull morphology advocates a generalist diet that focuses primarily on small prey and includes fishing, and suggest that in the skeleton of the baryonyx , which is also assigned to the spinosaurids, parts of a young iguanodon , i.e. a land-dwelling herbivore, were found. Naish et al. 2004 also share this assumption for Irritator and show that, as a generalist, he hunted both aquatic and terrestrial prey in coastal areas and also probably looked for carrion.
Especially with Irritator and Suchomimus , a convergence to crocodiles is regularly discussed, which is even eponymous with Suchomimus (= "crocodile imitator"). In the past, individual fossils of the spinosaurids were even mistakenly mistaken for crocodile fossils and described, for example baryonyx fossils from Portugal, which were originally described as Suchosaurus and were only recognized as baryonyx in 2007 . With the exception of the skull, however, there are no convergences with crocodiles in the physique of the known spinosaurids, so that a general adaptation to an aquatic way of life is excluded.
Systematics
Irritator challengeri was classified by its first description in 1996 in the Maniraptora within the Tetanurae . Here they should be a separate family Irritatoridae within the Bullatosauria . Angaturama , on the other hand, was classified as a new genus in the Spinosauridae and in the same year Kellner also classified Irritator in this family. This classification was adopted by Sues et al. 2002 also for the fossils now recognized as synonyms, so that they are now generally accepted.
Paul Sereno et al. In 1998, when Suchomimus tenerensis was first described, presented a phylogenetic tree of the Spinosauridae, which divided them into the two subfamilies Spinosaurinae and Baryonychinae and defined Irritator as a sister species of the genus Spinosaurus . This representation was confirmed by dal Sasso et al. 2006. According to this, Suchomimus and Baryonyx , whose only representative Baronyx walkeri was described from England in 1986, together form the Baryonychinae, while Irritator and Spinosaurus were compared to these as Spinosaurinae. Sasso et al. add the Cristatusaurus lapparenti described in 1998 to the Baryonychinae , which in the original description by Sereno et al. was not yet described. As a sister group of the entire Spinosauridae, the Torvosauridae are named with the genera Torvosaurus and Eustreptospondylus , which are now included in the Megalosauridae .
| Spinosauridae |
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This family tree is justified primarily by features of the skull morphology, since this part of the skeleton is at least partially present in most species. The Spinosauroidea are primarily justified by the formation of the strong front limbs with a sickle-like thumb claw.
The extension of the snout region, which was carried out as a specialization in fishing, by a parallel extension of both the maxillary and the premaxillary , the specific design of the nasal cavity and the formation of a secondary roof of the mouth are very important independent features ( apomorphies ) that secure the monophyly of the Spinosauridae. Features such as the nostrils shifted far back and the conical teeth, a small post-nasal cranial window and the specific design of the cranium, which is relatively short compared to other theropods, but deeply formed are also listed here. In the Spinosaurinae there was a reduction in the number of premaxillary and maxillary teeth with an associated increase in the distance between the teeth and an almost straight formation of the teeth, which is present in both Irritator and Spinosaurus . In comparison to Irritator, Spinosaurus is mainly justified by the strong enlargement of the spinous processes of the spine and the resulting dorsal sail - how these looked like in the Irritator is not known.
reconstruction
Although Irritator only has one skull after joining the two known fossils, a relatively realistic reconstruction of the entire animal is possible. In this case, the paleontologists benefit greatly from the species that are classified as closely related to the Irritator and of which very complete skeletons exist or have existed (the Spinosaurus skeleton kept in Munich was destroyed in the Second World War). By comparing characteristics, many characteristics of Irritator can be assumed as plesiomorphies , i.e. characteristics that already exist in the common parent species - including above all the posture and design of the limbs as well as the general body structure and posture.
Since, for example, all fossil Theropoda were biped and living on land and this also applies to all other species of Spinosauroidea , these characteristics can also be assumed for the irritator - it is extremely unlikely that the irritator apomorphically developed these very central characteristics in a strongly modified form. Accordingly, almost all the characteristics that the closely related species Baryonyx , Spinosaurus and Suchomimus have in common can be assumed to exist with a very high probability than in Irritator - this enables a basic reconstruction. On the other hand, it is not possible, for example, to safely assume a back sail that has only been proven for Spinosaurus ; However, since Suchomimus also had strongly elongated spinous processes, at least this characteristic can also be assumed for Irritator .
Naming
Martill et al. described both the genus and the so far only known species within the genus in their article published in 1996. The naming of the genus Irritator was justified by the authors with the irritation they felt when they noticed the artificial elongation of the fossil's snout. Name derives from the nature of the fictional Professor Challenger, was in Sir Arthur Conan Doyle's novel " The Lost World " ( "The Lost World"), which Irritator as a second type next to the pterosaur arthurdactylus conandoylei , which is also in the Santana Formation was found in its designation indicates Conan Doyle.
Angaturama was chosen by Kellner and Campos for the name of the fossil they described because the word in the Tupí language stands for “noble”. The epithet limai is a tribute to the work of the Brazilian paleontologist Murilo Rodolfo de Lima , who found the fossil and gave it to the first person to describe it.
supporting documents
Cited evidence and footnotes
Most of the information in this article is taken from the sources given under Literature; the following publications are also cited:
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ 2010, ISBN 978-0-691-13720-9 , p. 88, Online ( Memento of the original of July 13, 2015 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ↑ Jonathas de Souza Bittencourt, Alexander WA Kellner: On a sequence of sacrocaudal theropod dinosaur vertebrae from the Lower Cretaceous Santana Formation, Northeastern Brazil. In: Arquivos do Museu Nacional. Rio de Janeiro. Vol. 62, No. 3, 2004, ISSN 0365-4508 , pp. 309-320, ( abstract ( memento of August 2, 2012 in the web archive archive.today )).
- ↑ a b Alexander WA Kellner, Diogenes A. Campos: First Early Cretaceous theropod dinosaur from Brazil with comments on Spirosauridae. In: New Yearbook for Geology and Paleontology. Treatises. Vol. 199, 1996, ISSN 0077-7749 , pp. 151-166.
- ^ Alan J. Charig , Angela C. Milner : Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. In: Bulletin of the British Museum (Natural History). Geology Series. Vol. 53, No. 1, 1987, ISSN 0007-1471 , pp. 11-70, digitized .
- ↑ a b c Paul C. Sereno , Allison L. Beck, Didier B. Dutheil, Boubacar Gado, Hans CE Larsson, Gabrielle H. Lyon, Jonathan D. Marcot, Oliver WM Rauhut , Rudyard W. Sadleir, Christian A. Sidor, David D. Varricchio, Gregory P. Wilson, Jeffrey A. Wilson: A Long-Snouted Predatory Dinosaur from Africa and the Evolution of Spinosaurids. In: Science . Vol. 282, No. 5392, November 13, 1998, pp. 1298–1302, doi : 10.1126 / science.282.5392.1298 , full text (PDF; 393 kB) .
- ↑ Alexander WA Kellner, Diogenes A. Campos: Brief Review of Dinosaur Studies and Perspectives in Brazil. In: Anais da Academia Brasileira de Ciências. Vol. 72, No. 4, 2000, ISSN 0001-3765 , pp. 509-538, full text (PDF; 988 kB) .
- ↑ Elaine Batista Machado, Alexander WA Kellner: Notas Sobre Spinosauridae (Theropoda, Dinosauria). In: Anuário do Instituto de Geociências. Vol. 28, No. 1, 2005, ISSN 0101-9759 , pp. 158-173, full text (PDF; 375 kB) .
- ↑ Ren Hirayama: Oldest known sea turtle. In: Nature . Vol. 392, No. 6677, 1998, pp. 705-708, doi : 10.1038 / 33669 .
- ↑ a b Eric Buffetaut : The spinosaurid dinosaur Baryonyx (Saurischia, Theropoda) in the Early Cretaceous of Portugal. In: Geological Magazine. Vol. 144, No. 6, 2007, ISSN 0016-7568 , pp. 1021-1025, doi : 10.1017 / S0016756807003883 .
- ↑ Darren Naish, David M. Martill, Eberhard Frey: Ecology, Systematics and Biogeographical Relationships of Dinosaurs, Including a New Theropod, from the Santana Formation (? Albian, Early Cretaceous) of Brazil. In: Historical Biology. Vol. 16, No. 2, 2004, pp. 57-70, doi : 10.1080 / 08912960410001674200 .
- ↑ a b Thomas R. Holtz Jr .: Spinosaurs as Crocodile Mimics. In: Science. Vol. 282, No. 5392, November 13, 1998, pp. 1276-1277, doi : 10.1126 / science.282.5392.1276 .
- ↑ Alexander WA Kellner: Remarks on Brazilian dinosaurs. In: Memoirs of the Queensland Museum. Vol. 39, No. 3, 1996, ISSN 0079-8835 , pp. 611-626.
- ↑ Cristiano Dal Sasso , Simone Maganuco, Eric Buffetaut, Marco A. Mendez: New information on the skull of the enigmatic theropod Spinosaurus , with remarks on its sizes and affinities. In: Journal of Vertebrate Paleontology. Vol. 25, No. 4, 2005, pp. 888-896, doi : 10.1671 / 0272-4634 (2005) 025 [0888: NIOTSO] 2.0.CO; 2 .
- ^ Alan J. Charig, Angela C. Milner: Baryonyx, a remarkable new theropod dinosaur. In: Nature. Vol. 324, No. 6095, 1986, pp. 359-361, doi : 10.1038 / 324359a0 .
- ^ Philippe Taquet , Dale A. Russell : New data on spinosaurid dinosaurs from the Early Cretaceous of the Sahara. In: Comptes Rendus de l'Académie des Sciences. Series IIA: Earth and Planetary Science. Vol. 327, No. 5, 1998, pp. 347-353, doi : 10.1016 / S1251-8050 (98) 80054-2 .
- ↑ David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 .
- ↑ "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated". Quote Martill et al. 1996.
- ^ "From Prof. Challenger, the ficticious hero and dinosaur discoverer of Sir Arthur Conan Doyle's Lost World". Quote Martill et al. 1996.
literature
- David M. Martill, Arthur RI Cruickshank, Eberhard Frey , PG Small, M. Clarke: A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. In: Journal of the Geological Society. Vol. 153, No. 1, 1996, ISSN 0016-7649 , pp. 5-8, doi : 10.1144 / gsjgs.153.1.0005 .
- Hans-Dieter Sues , Eberhard Frey, David M. Martill, Diane M. Scott: Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. In: Journal of Vertebrate Paleontology. Vol. 22, No. 3, 2002, ISSN 0272-4634 , pp. 535-547, doi : 10.1671 / 0272-4634 (2002) 022 [0535: ICASDT] 2.0.CO; 2 .
